Manufacture of nickel-plated steel



Jan. 17, 1956 M. M. RUBIN 2,731,403

MANUFACTURE OF NICKEL-PLATED STEEL Filed Nov. 8, 1952 2 Sheets-Sheet l BASE METAL (STEEL CONTAINING 264.50% C) MORE OR LESS TEMPERED NICKEL PLATE ANNEAL FABRICATE HEAT TREAT HEAT TREAT PRODUCT NO. PRODUCT NO. 2 NICKEL PLATED NICKEL PLATED HEAT TEMPERED TEMPERED SPRING STEEL SPRING STEEL mmvroza.

MICHAEL M. RUBIN ti/(MM; 0W

ATTORNEYS Jan. 17, 1956 M. M. RUBIN MANUFACTURE OF NICKEL-PLATED STEEL 2 Sheets-Sheet 2 Filed-Nov. 8. 1952 INVENTOR. M/GHAEL M. RUB/IV AT'TUR/VEYS United States Patent v 2,731,403 MANUFACTURE OF NICKEL-PLATED STEEL Michael M. Rubin, Warren, Ohio, assignor to Pittsburgh Steel Company, Pittsburgh, Pa., a corporation of Penn= sylvania Application November 8, 1952, Serial No. 319,549

4 Claims. (Cl. 204-37) This invention relates, as indicated, to methods of coating ferrous metals with nickel, but has reference more particularly to the coating of hardenable carbon steel and alloy steel rolled and drawn products, such as strip and wire, whereby a ductile, non-porous, uniform and intimately bonded coating of nickel is formed on such carbon steel or alloy steel, and whereby embrittlement of the steel is avoided.

It has heretofore been the practice to nickel-coat or nickel-piate steel products containing in excess of .25% carbon, but in all instances of which I am aware, the coating or plating of the nickel has been applied after the products have been hardened by heat treatment or other methods.

When the nickel plating is thus applied to the finished product, the product, in most instances, is characterized by a poor or defective bonding of the nickel to the hardened steel, by embrittlernent of the nickel-coated steel due to absorption or occlusion therein of hydrogen generated during the coating or plating operation, and by a certain degree of residual stress and porosity of the coating, which render the coating subject to corrosion factors and therefore less protective to the base metal.

The problem of embrittlement of the nickel-coated steel due to absorption or occlusion therein of hydrogen generated during the coating or plating operation is well known and is a particularly aggravating one. Probably the best general statement is found in an editorial entitled Hydrogen Embrittlcment from Plating in Metal Finishing, September, 1941, vol. 39, page 469.. This article discusses the factors involved, methods for reducing hydrogen absorption, and procedures for relief of embrittlement.

In one procedure, substantiated by several years of production application, such embrittlement is minimized during the plating operation and relieved by a heat treatment of 2 /2 hours at 527 F., well below the normal tempering temperature.

These embrittlement-relieving heat treatments, it may be emphasized, are. designed to relieve embrittlement after it has occurred, and the temperatures are limited to a range below those at which the properties of the steel might be affected. In contrast, the process of this application, as will appear hereinafter, removes hydrogen before the steel is hardened, and simultaneously With the heating operation prior to hardening, atmuch higher temperatures, and in a different sequence than taught by the prior art. 1

In my U. S. Patent No. 2,115,750, a method of coating strip steel and the like is disclosed, in which steel strip, such as tin plate stock, is plated with nickel and is then subjected to an annealing operation, in order to improve the bond between the nickel and steel, drive off occluded gases, such as hydrogen, render the coating more ductile and impervious, and, at the same time, cause an annealing of the steel base. The carbon content of the steel in such process, has usually been of the order of about .10%

or less, and in no event, has the carbon content been in excess of about .20%. It is Well known that ordinary carbon steels of such low carbon content, are, as a general rule, incapable of being hardened by heat treatment or other means to any appreciable degree for the purpose of changing or improving their physical properties or characteristics. The annealing, in other words, has resulted in a softening of the base metal, enabling it to be more easily formed or bent, for the purpose described in said patent, i. e., formation into containers for food and the like.

I have discovered, as the result of considerable experimentation, that similar improvements in the nickel coating can be effected in the case of nickel-coated or nickel-plated steel products in which the steel or base metal is of an analysis or composition enabling it to be hardened by heat treatment or other means so that such heat treatment can be efiected simultaneously with or incidental to the heating of the nickel coating, resulting in a product having desired properties, as to the base metal, coating, and the bond therebetween.

The steels to which our methods are applicable are genenerally classed as heat-treatable or hardenable steels, containing carbon in amounts of from .26% to 1.50%. This includes those steels which, according to Websters New International Dictionary, Second Edition, are classified as medium-carbon (roughly 0.25 to 0.60% carbon), called medium steel, and high-carbon (roughly more than 0.60% carbon), called hard. steel. It also comprises all steels which are characterized by the ability to be hardened by cooling or quenching from above a certain temperature, generally known as the critical point of the steel. According to Webster, all steels except low carbon steels, which he defines as steel with less than .25 carbon, and termed mild or soft steel, have this hardening characteristic.

Such low carbon steels are accordingly excluded from the scope of this invention, except that so-called alloy steels, which, in some instances, may contain less than .26% carbon, are included within the scope of the invention. In these so-called alloy steels, hardenability and other characteristics may be obtained by the inclusion therein of certain elements, such as chromium, vanadium, etc., so that the steel, in some cases, may contain less than .26% carbon. For purposes of the present invention, a steel is classed as alloy steel when the maximum of the range given for the content of alloying elements exceeds one or more of the following limits: manganese, 1.65 percent; silicon, 0.60 percent; copper, 0.60 percent; or in which a definite range or definite minimum quantity of any of the following elements is specified or required within the limits of the recognized commercial field of alloy steels; aluminum, boron, chromium up to 3.99 percent, cobalt, columbium, molybdenum, nickel, titanium, tungsten, vanadium, zirconium, or any other alloying ele: ment added to obtain a desired alloying effect (Steel Products Manual, Hot Rolled Alloy Steels, Section 10, American Iron and Steel Institute, 350 Fifth Avenue, New York 1, N. Y., July, 1947, part ll, page 4).

Since the present invention is thus concerned only with steel or alloy steel, the term steel implying the presence of some carbon in the metal, certain prior art disclosures, such as the core wire described in Hoyt Patent 1,547,395, consisting of 59% iron and 41% nickel, are excluded from the scope or purview of the invention.

In its more specific aspects, the present invention is concerned more particularly with the plating and treatment of so-called spring steels, which are adapted for fabrication or forming into springs of various types, such as flat springs, leaf springs, helical springs, etc., and which usually contain from about .40% to about 1.10% carbon. One advantage of the process over prior art processes is that it produces a nickelplated spring steel that is less subject to corrosion fatigue than nickel-plated spring steel made by plating previously tempered steel.

The various methods which may be employed in the fabrication of springs in accordance with our invention are illustrated more or less diagrammatically in Fig. l of the accompanying drawings.

The base metal, in each instance, and, as shown in Fig. 2 of the accompanying drawings, is drawn from a coil and is passed successively through an alkali cleaning tank 1, a rinse tank 2, an acid pickling tank 3, another rinse tank 4, a nickel plating tank 4, another rinse tank 6, and a drying oven 7. In this way, a nickel plating of desired thickness is applied to the strip or wire. The nickel coating, however, is not positively bonded to the base metal, the steel base is characterized by a mild degree of embrittlement, due to absorption or occlusion therein of hydrogen gas evolved during the plating operation, and the coating has a certain degree of stress, strain and porosity which render the platingsubject to corrosion factors.

Following the plating operation, the nickel-coated steel strip or wire may be subjected to one of various heat treatments, each of which is designed to not only bring about a marked change in the physical properties of the'base metal, but to also simultaneously effect improvements in the properties of the nickel coating and in the bond between the nickel coating and the base metal. In each treatment, the plated strip is heated for a sufiicient length of time at a temperature suflicient to eifect transformation of the crystalline structure of the steel, after which the strip is quenched or cooled at a rate which depends on the composition of the steel, and in accordance with procedures which are well known in the art of heat treating.

While the transformation range is a fairly broad one, I have found that a highly practical and fairly critical range, within such broader range, is from about 1450 F. to about 1650 F. By heating to at least the lower limit of this critical range, insurance is had that transformation will take place, irrespective of the loss of heat which usually occurs incidental to the manipulation or handling of the strip between the heating thereof and the initiation of the quenching or cooling of the strip. By restriction of the upper limit of this critical range to about 1650 R, an undesirable degree of diffusion of the nickel intothe base metal is avoided.

Examples of such treatments are given below, with reference to the above flow diagram or chart:

Example 1 Nickel plated steel strip, /2" wide and .005" thick,

containing .90-l.05% carbon and 30-50% manganese, was passed continuously through a furnace approximately 20 feet long, at a temperature of 1600 F., the speed of the strip through the furnace being 33 feet per minute. This brought about a desired heating of the steel placing it in the austenitiocondition for subsequent hardening, and caused a diffusion of the nickel and steel into one another, forming a solid solution zone at their contiguous surface, tenaciously uniting the nickel and steel. The nickel coating was also rendered ductile, free from internal stresses and strains and relatively free from pin holes, the occluded hydrogen and other occluded gases being driven ofi, so that the nickel-plated steel could be hardened without embrittlement.

. Following this heating step, the strip was quenched by passing it through water-cooled tungsten carbide blocks to'harden it, and was then passed through a tempering or drawing furnace to develop the desired physical properties. The length of the tempering furnace was about 20 feet, and the furnace was maintained at a temperature of 750 F., the strip traveling through the furnace at a speed of 33 feet per minute.

The base metal, after cooling, had a Rockwell hardness of 85, on N scale.

The resultant material which was typical of the heattempered product No. 1 produced in accordance with the first column of the diagram in Fig. 1, was nickel-plated heat tempered spring steel, adapted for fabrication into many varieties of springs.

The nickel-plated strip, throughout the aforesaid treatment, is maintained in a neutral or reducing atmosphere, provided by suitable gases, whereby oxidation of the metals is precluded at all times.

Example 2 Nickel-plated steel strip, 1" wide and .040" thick, containing .59.7l% carbon and .60.90% manganese, was passed through a furnace approximately 30 feet long, at a temperature of 1550 F., and at a speed of 8 feet per minute. This brought about a desired heating of the steel as well as the other efiects described in Example 1. Following this heating step, the strip was quenched in oil to harden it, and then passed through a tempering or drawing furnace 30 feet long, ata temperature of 850-900 F., at a speed of 8 feet per minute. The base metal, after cooling, had a hardness of about 50 Rockwell C scale.

The resultant material which was also a heat-treated product produced in accordance with the first column of the diagram in Fig. 1, was nickel-plated heat-tempered spring steel, adapted for fabrication into various types of springs.

, Example 3 This is an example of a batch treatment, in contrast to the continuous treatment, as described in Examples 1 and 2. Nickel-plated strip, in the form of coils, and

of the same dimensions and analysis as in Example 2,

was annealed at a temperature of 1280 F. for 36 hours, and slowly cooled in the annealing furnace to a temperature of 1100 F., a non-oxidizing atmosphere being maintained in the furnace throughout.

The strip was then cooled to atmospheric temperature and fabricated or formed into parts of various kinds, which were then heat-tempered, i. e., heated at about 1500 F. for about ten minutes, then quenched in oil, and then drawn at a temperature of 850 F.-900 F.

. for about one-half hour. This provided products typical of product No. 2 in Fig. 1.

Example 4 Nickel-plated steel strip of the same dimensions and analysis as in Example 3, was annealed as described in Example 3, and then fabricated and heat treated as indicated in the second column of the diagram in Fig. 1, to provide a product typical of product No. 2 in Fig. 1.

Example 5 This is an example of the method as applied to a typical alloy steel adapted for fabrication into springs and the like. The steel was A. I. S. I. 4130 (a chrome molybdenum alloy steel), having the following analysis:

Carbon .28-.33 Manganese .40-.60 P and S .04max.

Silicon .20-.35 Chromium .801.10 Molybdenum .l5.25

to the manufacture of spring stock, it is to be understood that the methods are equally adaptable and useful for the manufacture of steel strip and wire stock for other pur* poses, such, for example, as metal tapes or rulers, razor blades, cutlery, etc.

Other modes of applying the principles of my invention may be employed instead of those explained, changes being made as regards the methods herein disclosed, provided the step or steps stated by any of the following claims or the equivalent of such stated step or steps be employed.

This application is a continuation-in-part of my copending application, Serial No. 97,720, filed June 8, 1949, and now abandoned.

I therefore particularly point out and distinctly claim as my invention:

1. The method of making a coated steel product from hardenable steel selected from the group consisting of plain carbon steels containing from .26% to 1.50% carbon and alloy steels which are hardenable by being heated to a temperature within the range of from about 1450 F. to about 1650 F., said method comprising electro-depositing a coating of nickel on said steel, subjecting the coated steel to a treatment in which the steel is hardened by being heated to a temperature within the range of from about 1450 F. to about 1650 F. and cooled, and then tempered, said treatment resulting in the formation of an intimate bonding of the nickel coating with the steel, which is then substantially free from embrittlement, a hardening of the steel, and the develop ment of desired physical properties in the steel.

2. The method, as defined in claim 1, in which the cooling is efiected by quenching of the steel.

3. The method of coating steel which is hardenable by quenching from a temperature above its critical point, said steel selected from the group consisting of plain carbon steels containing from .26% to 1.50% carbon and alloy steels which are hardenable by being heated to a temperature within the range of from about 1450" F. to about 1650 F., said method comprising the steps of electro-depositing a coating of nickel on the steel, then heating to a temperature of from about 1450 F. to about 1650 F., until transformation is completed, then cooling the steel at a predetermined rate by quenching it and then tempering the steel, whereby to effect a distinct change in the properties of the steel and an improvement in the bond between the nickel and steel, and relieving stresses in the steel and nickel deposit.

4. In a process for making nickel-plated spring steel, said steel selected from the group consisting of plain carbon steels containing from .26% to 1.50% carbon and alloy steels which are hardenable by being heated to a temperature within the range of from about 1450 F. to about 1650 B, said process comprising the steps of first electro-plating the spring stock with nickel, and then developing the desired temper in the steel by heat treating, cooling and drawing operations, in which the heat treating is within the temperature range of from about 1450" F. to about 1650 F, thereby avoiding the embrittlement of the steel normally resulting from a reversal of the sequence of these steps.

References Cited in the file of this patent UNITED STATES PATENTS 1,934,741 Schulein Nov. 14, 1933 2,402,834 Nachtman June 25, 1946 2,534,911 Kasper Dec. 19, 1950 2,683,835 Freedman July 13, 1954 FOREIGN PATENTS 624,252 Great Britain s ssssss May 31, 1949 

1. THE METHOD OF MAKING A COATED STEEL PRODUCT FROM HARDENABLE STEEL SELECTED FROM THE GROUP CONSISTING OF PLAIN CARBON STEELS CONTAINING FROM 26% TO 1.50% CARBON AND ALLOY STEELS WHICH ARE HARDENABLY BY BEING HEATED TO TEMPERATURE WITHIN THE RANGE OF FROM ABOUT 1450* F. TO ABOUT 1650* F., SAID METHOD COMPRISING ELECREO-DEPOSITING A COATING OF NICKEL ON SAID STEEL, SUBJECTING THE COATED STEEL TO A TREATMENT IN WHICH THE STEEL IS HARDENED BY BEING HEATED TO A TEMPERATURE WITHIN THE RANGE OF FROM ABOUT 1450* F. TO ABOUT 1650* F. AND COOLED, AND THEN TEMPERED, SAID TREATMENT RESULTING IN THE FORMATION OF AN INTIMATE BONDING OF THE NICKEL COATING WITH THE STEEL, WHICH IS THEN SUBSTANTIALLY FREE FROM EMBRITTLEMENT, A HARDENING OF THE STEEL, AND THE DEVELOPMENT OF DESIRED PHYSICAL PROPERTIES IN THE STEEL. 